Maybe it's a bit cliche, but as a lover of all language-related things, I'm not a big fan of math.

I may even, at less mature moments in life, have said something along the lines of, "I hate math." Or "math sucks."

Now that I'm older, I can accept that math is not such a horrible thing... we just don't mesh well 100% of the time.

And I have messed up when trying to discuss math-related topics in Japanese quite a few times, as well.

Take the following conversation, for example...

A:
これ5個買ったらいくら？
これ　ごこ　かったら　いくら？
How much would it cost if we bought five of these?
Literally: "this + five (little) things + if bought + how much?"

B:
えーっと.....わかんない、数学苦手！
えーっと..... わかんない、 すうがく　にがて！
Uh, let's see... I don't know. I'm not good at math!
Literally: "Hmm... + I don't know. + math + poor at."
Note: えーっと is like saying "Hmm" or "Umm" or "Let's see" when you're trying to think of the answer to something. For more on this usage of 苦手, check out [NDL #47] - My Bitter Lack of Skills.

A:
数学じゃなくて算数だよ！
すうがく　じゃ　なくて　さんすう　だ　よ！
It's not "math;" it's simple arithmetic!
Literally: "math + is not + (simple) arithmetic + is + よ！"
Note: 算数 is the math studied in elementary school; 数学 is math from middle school onward.

Rei and I have had a conversation just like this one several times.

As you might have guessed, I'm Person B.

For some reason, my brain just has trouble separating 算数 and 数学... probably because we just say "math" in English.

To clarify my understanding of the differences between these two words, I turned to my old friend, Google Images.

Here we have 算数（さんすう // [simple] arithmetic）：

And here we have 数学（すうがく // mathematics）：

I'm pretty sure I was still at the 算数 level in middle school, but Japanese schools are notorious for having high standards for math.

OK. Time to get serious...

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Here is our guide for dictating mathematical equations...

Use たす for addition.

1 PLUS 1
↓　↓　↓
1 たす 1

Use ひく for subtraction.

3 MINUS 2
↓　↓　↓
3 ひく 2

Use かける for multiplication.

2 TIMES 2
↓　↓　↓
2 かける 2

Use わる for division:

8 DIVIDED BY 4
↓　↓　↓
8 わる 4

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Examples...

1+1=2
いち　たす　いち　は　に
One plus one is two.
Literally: "one + add + one + は + two."

10-6=4
じゅう　ひく　ろく　は　よん
Ten minus six is four.
Literally: "ten + pull [subtract] + six + は + four."

10×100=1000
じゅう　かける　ひゃく　は　せん
Ten times one hundred is one thousand.
Literally: "ten + multiply + one hundred + は + one thousand."

60÷5=12
ろくじゅう　わる　ご　は　じゅうに
Sixty divided by five is twelve.
Literally: "sixty + divide + five + は + twelve."

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Oh, and one more very confusing fact is that they say fractions in the opposite order, like this:

2/5
ご　ぶん　の　に
Two-fifths.
Literally: "five + parts + の + two."

So that's:
DENOMINATOR ぶんの NOMINATOR

In other words:
[Bottom Number] ぶんの [Top Number].

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Bonus Interesting Stuff

You know how we use かける for multiplication? Well we saw about 2 million other ways to use this word in this lesson: [NDL #104] - Hanging Calls

Also, the kanji for ぶん in ぶんの (for fractions, above) is 分, meaning "part." Makes sense.

Also, the kanji for the word わる (used for division) is 割る (わる // to divide; to cut; to split). This kanji shows up in the word 割引 (わりびき // discount). I guess when you "divide" a price and then "pull" (or SUBTRACT!) some of it away, you're giving a discount.

Last but not least, the kanji for たす (used for addition), is 足す (たす // to add). You also see this kanji in the intransitive verb 足りる (たりる // to be sufficient; to be enough). Oh, and by itself, 足 (あし) means "foot" or "leg," but I'm not sure what that has to do with addition.

Good luck with all of this number stuff. If I figured it out, surely you can too. ^^